Infinitely variable torque ratio characteristics for a power transmission can be achieved by using a friction belt and pulley arrangement in which a drive pulley and a driven pulley, connected by an endless belt, are adapted for torque transfer with an infinitely variable torque ratio range by adjusting the pitch diameter of the pulleys, the pitch diameter of the driving pulley increasing as the pitch diameter of the driven pulley decreases, and vice versa. Examples of belt drives of this kind may be seen by referring to U.S. Pat. Nos. 5,417,621 and 5,514,047.
It is known design practice also to provide infinitely variable torque ratio characteristics by using a hydraulic pump as a driving member and a hydraulic motor as a driven member. The pump and motor are located in a closed hydrostatic fluid pressure circuit. By varying the displacement of the pump, the effective speed ratio of the hydrostatic transmission can be changed through a wide torque ratio range.
Various types of infinitely variable friction drives also are well known. It is known design practice, for example, to use friction cone members wherein the relative positions of the friction cones are adjustable to provide an infinitely variable torque ratio characteristic. An example of a friction cone drive mechanism may be seen by referring to U.S. Pat. No. 5,681,235.
If an infinitely variable transmission is used with an internal combustion engine to deliver torque to driven members, such as vehicle traction wheels, the infinitely variable transmission characteristics can be matched with the engine speed/torque characteristics such that the engine may be operated with an engine throttle setting that will correspond to a speed consistent with minimum brake specific fuel consumption as variable torques are commanded by the operator. In this way, the continuously variable transmission improves the overall driveline efficiency.